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Docker

Prerequisites

The only prerequisites are:

  1. This repo, and
  2. Docker

Building the docker image pulls in all the dev dependencies to build loop within the image itself. Having a go development environment is not required.

Building the Docker Image

The docker image can be built using this command within the loop directory:

docker build --tag loop .

This command pulls down a go build container, builds loop and loopd executables, then publishes those binaries to a fresh, smaller image, and marks that image with the tag 'loop'.

Running the Docker Image

The docker image contains:

  • The binary loopd, at /go/bin/loopd
  • The binary loop, at /go/bin/loop

Docker is very flexible so you can use that information however you choose. This guide isn't meant to be prescriptive.

### Example: Running loopd

One way of running loopd is

docker run --rm -it --name loopd -v $HOME/.lnd:/root/.lnd -v $HOME/.loop:/root/.loop loop:latest loopd --network=testnet --lnd.host <my-lnd-ip-address>:10009

Things to note from this docker command:

  • You can stop the server with Control-C, and it'll clean up the associated stopped container automatically.
  • The name of the running container is 'loopd' (which you may need to know to run the loop command).
  • The '.lnd' directory in your home directory is mapped into the container, and loopd will look for your tls.cert and macaroon in the default locations. If this isn't appropriate for your case you can map whatever directories you choose and override where loopd looks for them using additional command-line parameters.
  • The '.loop' directory in your home directory is mapped into the container, and loopd will use that directory to store some state.
  • You probably need to specify your LND server host and port explicitly, since by default loopd looks for it on localhost and there is no LND server on localhost within the container.
  • No ports are mapped, so it's not possible to connect to the running loopd from outside the container. (This is deliberate. You can map ports 8081 and 11010 to connect from outside the container if you choose.)

Example: Running loop

If you're using the example above to run loopd, you can then run the loop command inside that running container to execute loops. One way would be:

docker exec -it loopd loop out --channel <channel-id-you-want-to-use> --amt <amount-you-want-to-loop-out>

Things to note about this docker command:

  • docker exec runs a command on an already-running container. In this case docker exec loopd says effectively 'run the rest of this command-line as a command on the already-running container 'loopd'.
  • The -it flags tell docker to run the command interatively and act like it's using a terminal. This helps with commands that do more than just write to stdout.
  • The remainder loop out --channel <channel-id-you-want-to-use> --amt <amount-you-want-to-loop-out> is the actual loop command you want to run. All the regular loop documentation applies to this bit.

A Handy Script

If you're using the example above to run loopd, creating a script can simplify running loop.

Create a file with the following contents:

#!/usr/bin/env bash
TERMINAL_FLAGS=
if [ -t 1 ] ; then
        TERMINAL_FLAGS="-it"
fi

docker exec $TERMINAL_FLAGS loopd loop "${@}"

Call this script 'loop', put it somewhere in your $PATH, and make it executable. Then you can just run commands like:

loop out --channel <channel-id-you-want-to-use> --amt <amount-you-want-to-loop-out>

without having to remember (or use) the docker part explicitly.

Caveats

Running loopd the way shown above won't restart loopd if it is stopped or if the computer is restarted. You may want to investigate running the 'loop' container at startup, or when your LND server starts. (For example, docker has restart options, or grouping of containers via docker-compose.)